Structural and Magnetic Dynamics in the Magnetic Shape Memory Alloy Ni$_2$MnGa

TL;DR

This study investigates the ultrafast structural and magnetic dynamics in Ni$_2$MnGa, revealing timescales of phase transitions, phonon modes, and demagnetization using time-resolved x-ray and magneto-optical techniques.

Contribution

It provides the first detailed measurement of the intrinsic timescales of structural and magnetic changes in Ni$_2$MnGa during laser excitation.

Findings

Ultrafast quenching of incommensurate modulation within 300 fs.

Demagnetization occurs in approximately 320 fs.

Martensitic transition proceeds via nucleation within a few ps.

Abstract

Magnetic shape memory Heusler alloys are multiferroics stabilized by the correlations between electronic, magnetic and structural order. To study these correlations we use time resolved x-ray diffraction and magneto-optical Kerr effect experiments to measure the laser induced dynamics in a Heusler alloy Ni$_2$MnGa film and reveal a set of timescales intrinsic to the system. We observe a coherent phonon which we identify as the amplitudon of the modulated structure and an ultrafast phase transition leading to a quenching of the incommensurate modulation within 300~fs with a recovery time of a few ps. The thermally driven martensitic transition to the high temperature cubic phase proceeds via nucleation within a few ps and domain growth limited by the speed of sound. The demagnetization time is 320~fs, which is comparable to the quenching of the structural modulation.